In copending application Ser. No. 214,189, filed on Dec. 8, 1980 and entitled "Method and Apparatus for Repairing Heat Exchanger," now U.S. Pat. No. 4,393,564, there is disclosed an expandable plug assembly and associated actuating apparatus for use in installing the plug assembly in a heat exchanger tube. The plug assembly comprises a radially deformable sleeve adapted to be placed in the tube of a heat exchanger in alignment with its tube sheet and an elongated wedge slidably received within the sleeve for expanding the sleeve outwardly when pulled axially relative to the sleeve. A breakaway member is mounted at the narrow end of the wedge and is connected to a pull rod which cooperates with a compression tube engaging the sleeve to pull the wedge into the sleeve and expand it outwardly to provide a fluid tight joint. After a predetermined amount of outward pressure has been applied, the breakaway ruptures to permit removal of the pull rod and compression tube from within the plugged tube.
In U.S. application Ser. No. 311,912, filed on Oct. 16, 1981 and entitled "Plug Assembly For Use in Method and Apparatus for Repairing Heat Exchangers," there is disclosed an expandable plug assembly which is particularly suited for use in providing a fluid tight joint in a heat exchanger having a tube which may have a substantial amount of corrosion on its inner surface. The plug assembly in this application is characterized by a plurality of alternating cutting edges and grooves on the periphery of the plugged sleeve. The cutting edges sever the scale and displace it into the grooves when installed in the manner described in the previously mentioned application.
While each of the aforementioned plug assemblies and associated placement apparatus functions entirely satisfactory for its intended purpose, it has been found that in certain situations there may be a tendency for the plugs to loosen and thereby permit leakage. For instance, in heat exchangers associated with nuclear power plants, it is customary for the repaired portion of the heat exchanger to be stress relieved after repair work has been performed. In stress relieving the affected portion, heat is applied at temperatures which can cause the installed plug to loosen when the heat exchanger is subsequently placed in service. Because of this possibility, there is a demand for a plug assembly which is resistant to loosening even when subjected to distortions caused by thermal expansion and contraction.